In this homework you will perform a dihybrid cross focusing

In this homework, you will perform a di-hybrid cross focusing on two traits of pea plants: Seed Color (Yellow vs. Green) and Seed Coat (Smooth vs. Wrinkle). The Yellow vs. Green seed colors are coded by dominant Y and recessive y alleles, respectively; The Smooth vs. Wrinkle seed coats are coded by dominant S and recessive s alleles, respectively. The genes for seed color & seed coat are located on different chromosomes. Say, you cross a male Smooth-Green plant (SSyy) with a female Smooth-Yellow plant (SsYy). That is, you cross SSyy times SsYy. Please follow what we did in class, answer the following 2 questions and fill in the Punnett Square table. Due on the March 28 (Tuesday) in class. What are the genotypes in F_1? What are their ratio? What are the phenotypes in F_1? What are their ratio? The Punnett Square table for SSyy times SsYy. Please fill in the genotypes of pollens, eggs, & each offspring. (Note that you may not need to use all cells in the table).

Solution

Parents: YYSS and yyss

F1- YySs

Gametes:YS,Ys,yS,ys

YYSS(Yellow and smooth)

yyss(Green and wrinkled)

For genotypic ratio:

(1YY + 2Yy + 1yy) x (1SS + 2Ss + 1ss) = 1 YYSS + 2 YYSs + 1 YYss + 2YySS + 4YySs + 2 yySS + 1yySS + 2yySs + 1yyss

Hence Genotypic ratio: -1:2:1:2:4:2:1:2:1

That is, we expect a characteristic 1:2:1:2:4:2:1:2:1 ratio of the nine possible genotypes.

These nine genotypes can be grouped into four phenotypes, for example 1 YYSS + 2 YYSs + 2 YySS + 4 YySs = 9YS yellow smooth peas. The ratio of these phenotypes is of course 9:3:3:1.

Phenotypic ratio -9:3:3:1

	YS	Ys	yS	ys
YS	YYSS(Yellow and smooth)	YYSs(Yellow and smooth)	YySS(Yellow and smooth)	YySs(Yellow and smooth)
Ys	YYSs(Yellow and smooth)	YYss(Yellow and wrikled)	YySs(Yellow and smooth)	Yyss(Yellow and wrinkled)
yS	YySS(Yellow and smooth)	YySs(Yellow and smooth)	yySs(Green and smooth)	yySs(Green and smooth)
ys	YySs(Yellow and smooth)	Yyss(Yellow and wrinkled)	yySs(Green and smooth)	yyss(Green and wrinkled)